解析

however 作副词表转折：

• However impressive the speech was = No matter how impressive the speech was = No matter how beautiful
• however 可以直接修饰形容词/副词，等于 no matter how
• 此用法中 however 后不接逗号，紧跟形容词

另外两种常见用法：

• However, I still felt...（however 单独使用作插入语，须加逗号）
• However impressive the speech was, ...（however + adj./adv.，表让步，等同 no matter how）

易错点：与 Although/Though 混淆。although 后不接形容词，although impressive the speech was 语法错误。